As the circuit density in multilevel integrated circuit devices increases, the reduction of feature size in a semiconductor device is strongly required. But, there are fatal problems such as R(resistance)×C(capacitance) delay due to crosstalk between interconnect lines. Therefore, dielectric constant of interlayer insulating films should be lowered so as to decrease the RC delay as much as possible. For this purpose, there have been various attempts to develop low dielectric materials for use in the insulating film.
For example, polysilsesquioxanes having dielectric constant of approximately 2.5˜3.1 has replaced SiO2 having dielectric constant of 4.0 in chemical vapor deposition (CVD). Such polysilsesquioxanes can be also applied to a spin coating method due to its excellent planation property.
The polysilsesquioxanes as well as preparing methods thereof are well known in the art. For example, U.S. Pat. No. 3,615,272 discloses a method for preparing completely condensed soluble hydrogensilsesquioxane resins, which comprises the steps of condensing trichlorosilanes in a sulfric acid medium, and then washing the resulting resins with water or aqueous sulfuric acid. U.S. Pat. No. 5,010,159 discloses a method for synthesizing soluble condensed hydridosilicon resins, which comprises the steps of hydrolyzing hydridosilanes in an arylsulfuric acid hydrate-containing hydrolysis medium, and then contacting the resulting resins with a neutralizing agent. U.S. Pat. No. 6,232,424 describes a highly soluble silicone resin composition having excellent solution stability, which was prepared by hydrolyzing and polycondensing tetraalkoxysilane, organosilane and organotrialkoxysilane monomers in the presence of water and a catalyst. U.S. Pat. No. 6,000,339 teaches that a silica-based compound, which may be useful for improving the resistance and physical properties as well as thickness of a coating film, can be obtained from a reaction of a monomer selected from the group consisting of alkoxysilane, fluorine-containing alkoxysilane and alkylalkoxysilane and a titanium- or zirconium-alkoxide compound in the presence of water and a catalyst. U.S. Pat. No. 5,853,808 describes that silsesquioxane polymers that are useful for preparing SiO2-rich ceramic coatings can be obtained as the polymeric reaction products from the hydrolysis and condensation of organosilanes having a β-substituted alkyl group.
However, the prior polysilsesquioxane resins have not accomplished very low dielectric constant that is currently required for insulating film between interconnect layers in semiconductor devices. Additionally, they have been required to improve in mechanical properties, thermal stability, crack-resistance, and so on.